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Full text of "Diseases Of The Nose Throat And Ear"

248

THE EAR

two constrictions in the canal, one near the junction of the two parts and the
other in the osseous part. The meatus may be partially straightened by
traction of the auricle upwards, outwards and backwards. Deficiencies of the
cartilaginous meatus, the fissures of Santorini, may provide a pathway for
infection between the parotid gland, the external meatus and superficial
mastoid tissues.

The skin lining the external acoustic meatus is continuous with that of the
auricle. The main glandular elements, sebaceous glands, ceruminous glands

Fig. 125. Left auricle viewed from without. 1,
Helix; 2, Scapha (fossa of helix); 3, Antihelix;
4, Lobule; 5,^Antitragus; S^Tragus;.?, Cavum
conchae; 8, Fossa triaagularis (fossa of anti-
helix). The lymph glands connected with the
"auricle are shown.

Fig. 126. Right external auditory meatus. 1,
Bony part; 2, Cartilaginous part; 3, Tympanic
membrane; 4, Hair follicles and ceruminous
glands; 5, Introitus; 6, Meatal cartilage.

and the hair follicles-are contained in the cartilaginous, portion, none of these
structures being present in the bony portion. The skin is closely adherent to
the underlying tissue and for this reason furuncles in the cartilaginous portion
are extremely painful owing to the increased tension in the tissue. The blood
supply of the auricle is obtained from thp ^ip&rfjcial temporal and p@sjrior_
auricular arteries. Whilst the_meatus is also supplied by these vessels, it^
receives a supply in Its inner part from the ^^.js^^^^^c^a^s^^^^
maxillary artery. The veins accompany, the., arteries.

The nerves of the external ear are derived from 'four cranial neryes.,the
aurkulotemporal nerve from the mandibular divisioifof the trigeminal nerve,
the posterior auricular branch of the facial nerve, a branch (Jacobson!s)_.frgm
the glossopjiaryngeal pervfc, thejaLUjricularJbranch of the vagus nerve, and from
the cervical _pkxusjC2 and C3, through the great auricular nerve.

The tympanic membrane, or drumhead (Fig* 127), separates the external
meatus from" the middle ear and functionally is part of the middle ear. The
periphery of the drumhead is attached to an incomplete bony ring, the
annulos, which lies at the medial end of the external meatus. The ring is